A character code. This is an integer.
A character set. Legal values for set are
:gbk. Additionally, on Windows, set can be a valid Windows code page identifier.
The character represented by code. If code is not a legal code in the specified set, the return value is undefined.
Returns the character that has the code code (an integer) in the coded character set specified by set, or
nil, if that character is not represented in the Lisp character set. Note that a coded character set is not the same thing as an external format.
(+ (* 100 row) column)
(+ (* 256 first-byte) second-byte)
:sjis is Shift-JIS encoded in the same way. Strictly speaking, EUC and Shift-JIS are not coded character sets, but encodings of the JIS sets, but the encoding is easily expressed as an integer, so the same interface to it is used.
LispWorks User Guide and Reference Manual - 13 Feb 2015